This invention relates to coatings for plastics, and, more particularly, to a wettability enhancing coating for plastics.
In several types of chemical and medical test procedures, a liquid such as a body fluid must be reacted with individual reactants in a sequence of related but separate chemical reactions, and then the final product analyzed. Traditionally, such procedures have been performed by placing the fluid into a reaction tube or the like, adding the remaining reactants for the first reaction, and permitting the first reaction to proceed to completion. The further reactants for the second reaction are added, and the second reaction is permitted to proceed to completion. This stepwise operation can be repeated as many times as necessary, until a final reaction product is obtained for analysis. This technique is not particularly suitable for conducting measurements of reactions such as those that produce measurable light by chemiluminescence, because of the time required to conduct the final mixing and place the reaction tube into a light-measurement apparatus.
In an alternative approach better suited for the measurement of chemiluminescent reactions, a plastic test plate having multichambered test wells has been developed. A liquid test sample is placed into a sample receiving chamber which has a sloping wall, and mixed with reactants previously placed into the first chamber. Then the test plate is tilted so that the mixture flows along the sloping wall of the sample receiving chamber and into a reaction measurement chamber. The reaction measurement chamber is preferably cylindrical in shape with a flat bottom that is pressed against a piece of photographic film. The mixture from the sample receiving chamber mixes with additional reactants and the light-producing reaction occurs if the original test sample contained a chemical under test. The intensity of any resulting light is measured through the transparent flat bottom of the reaction measurement chamber.
In practice, it has been found that typical aqueous solutions such as a mixture of urine test fluid and the reactants in the sample receiving chamber do not readily flow along the sloping wall of the sample receiving chamber. The aqueous mixture does not wet the sloping plastic wall, and has a tendency to bead and not flow. Since the test plate is normally inside a measurement apparatus with opaque walls when the procedures are performed, the failure of the aqueous liquid to flow from the sample receiving chamber to the reaction measurement chamber may not be detected. The result is an apparent negative result, since no light output would be measured. Where the test sample actually contained the reactant under study, the test results would be incorrect. Thus, a potentially injurious condition in the subject who provided the test sample might go undetected.
There is therefore a need for an approach for improving the flowability of an aqueous liquid test sample along a plastic surface. Some such approaches are known, including the proprietary Sigmacoat.RTM. hydrophobic coating and Dow gas treatment, and the corona discharge procedure. The latter is widely used, but requires expensive apparatus. A better approach is needed. The present invention fulfills this need, and further provides related advantages.